This invention relates to a knife shield for use in driving tunnels. The term "tunnel" or "tunnels" used throughout this specification is intended to include galleries, trenches and similar elongated excavations.
Knife shields conventionally have a plurality of elongate knives (or planks) mounted side-by-side on a support frame, the knives defining a generally cylindrical shield. The knives can be advanced relative to the frame, either singly or in groups, to extend the tunnel. After all the knives have been advanced, the frame is advanced in a follow-up sequence. Difficulties arise when it is desired to change the direction of advance of such a knife shield, for example, where the required direction of advance follows a curved path, or where corrections have to be made to ensure that the shield follows the desired path. Known knife shields are steered by advancing a number of knives and simultaneously bracing these knives towards the tunnel wall, hydraulic bracing rams being used for this purpose. These hydraulic bracing rams bear against the support frame to effect a tilting of the frame, relative to the axis of the tunnel, in the required direction. Unfortunately, this method of steering is extremely inexact, unreliable and permits no precise control movements.
The main object of the invention is to improve the directional control and steerability of a knife shield and thus make it possible to carry out accurate control movements and directional corrections.